"""(a) The tertiary-mode structures in a ZF with velocity $U(x)$: numerical eigenmodes (color) versus analytic solutions (dashed contours). Here, $x$ is radial coordinate and $y$ is poloidal coordinate. The mode structures are different near the minimum and the maximum of $U$. (b) The corresponding growth rates.  The superscript """"N"""" stands for numerical eigenvalues, and """"A"""" stands for analytic results. The subscript """"R"""" refers to mode localized near the minimum of $U$ (""""runaway"""" mode), and """"T"""" refers to mode localized near the maximum of $U$ (""""trapped"""" mode). The terminology is explained in Ref. 1."""
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